This invention relates to sheet offsetting and registering apparatus and in particular to the offsetting and registering of sheets produced from automatic reproducing machines. More specifically it relates to a simple device which serves to transport copies produced from an automatic reproducing machine to an output station and collect them in an offset and registered fashion.
In the reproduction of sets of original documents in automatic reproduction machines, it is often desired to collect the finished sets such that a registered edge of successive sets are offset slightly each from the other. Typically stacking mechanism devised to accomplish this result have generally used a set stacking tray that is movable from one collecting position to another collecting position so that the deposited sheets or stack are slightly offset from each other. Frequently a reciprocating tray has been used which often is required to move so fast that the individual sets in the tray shift in position due to inertial and vibration effects. In addition, such devices are generally mechanically complicated requiring numerous rails, slides, switches and motors and the like which often times make the device somewhat unreliable.
U.S. Pat. No. 4,188,025 to Gusfafson describes an offset sheet stacking apparatus for use with a copier to selectively apply different velocity profiles to copy sheets to cause them to be delivered into offset stacks of copy sheets in a receptacle. Two rotatable rollers form a nip for propelling sheets to either of two stacking positions. At least one of the rollers is movable between two positions and in the first position imparts a first velocity profile to the sheets of the first set to move them seriatim to a first stacking position. In the second position the nip imparts a second velocity profile to the sheets of the second set to move them seriatim to a second stacking position.
In addition, in many automatic copying machines the geometry of the machine elements is such that with the paper path the copies produced have the image on the top side. Thus sequential copies enter the collecting tray with the copy or image side up. This is satisfactory if only a single copy of a single image is desired or if multiple copies of a single image is desired. In both cases, no distinction between sequential copies is required and all copies may be readily collected with the image side up. It is also satisfactory if the original documents fed to the copying machine are fed in reverse order, last or bottom sheet first and first or top sheet last. In this instance the collected set has the top sheet face up on top and the bottom sheet face up on the bottom of the set. However, in most instances of copying sets of documents, the set is face up with top sheet on the top and if copied according to normal procedures, the top sheet, number one, is copied producing a copy face up and a set so produced has sheet number one face up on the bottom and the last sheet face up on the top. It can therefore be seen that it is desired to obtain the copies in the same order as the original set so that in the set produced by the copying machine the last sheet is on the bottom of the set and the top sheet is on the top of the set, both being face up. In addition, in electronic printing it is also advantageous to be able to print from the first page to the last page in order since if you print from the last sheet to the first sheet the substance of the first to last pages must be stored in the printers memory thereby increasing the size and cost of the memory required.
This result may be accomplished in copying a set of sheets if the top sheet, number one sheet, is fed first to be copied and the copy produced which is image side up is inverted such that the image is on the bottom side. With copying of successive sheets of a set and inverting each copy the final set is collected face down with the top sheet on the bottom and the bottom sheet on the top.
A number of techniques have been used in the past for inverting sheets. Exemplary of the prior inverting devices are those that have long belt drives which drive the sheet up in a first direction and then back the sheet in an opposite direction using the original trailing edge as the leading edge.
U.S. Pat. No. 3,968,960 to Fedor et al describes a sheet inverting and stacking apparatus wherein the leading edge of a sheet is sensed at a particular location, the rotary inverter is actuated with a leading edge deflecting element engaging the leading edge to decelerate it and deflect it from its path to a stacking platform. The trailing portion of the sheet is conveyed by two belt conveyors at about its original velocity and moves past the leading edge as the leading edge is deflected around an arc by the rotary inverter so that the sheet eventually is rolled over and deposited in an inverted positon on the stacking tray or preceding sheet. With the difference in speed between the leading and trailing edges the lead edge engaging element is able to deflect the leading edge of a sheet downward as the belts urge the remaining portion of the sheet past the leading edge to cause inversion of the sheet.
With the difference in speed, the leading edge moving slower than the trailing edge, the lead edge is constantly driven against the deflecting element thereby increasing the probability of damage to the leading edge. While lead edge damage may not be a serious problem for heavyweight papers it can be a serious problem for the lighter weight papers in that the edges may be curled, bent or crushed thereby producing untidy and even misregistered sheets in a stack or set of sheets all of which lead to user disatisfaction.
Furthermore, since both the lead edge and trailing edge of the sheet are placed under stress in this type of apparatus there is the possibility of additional damage particularly for light weight paper, due to buckling, tearing and jamming.
It is also known to use continuously rotating wheels or drums which have slots, envelopes or other chambers on the periphery in which the leading edge of a sheet may be inserted as the wheel, disc or drum is rotated and the sheet is advanced into engagement with a slot opening. All these devices suffer the disadvantage that as the wheel moves, the sheet must catch up to the slot in the wheel before it is physically captured thereby increasing the probability of error in alignment of the sheet and even the possibility that the leading edge of the sheet will not be captured in the slot leading to a possible jamming of the sheet in the machine. Furthermore, with the sheet overtaking the slot the design typically allows the sheet to fully enter the slot such that the leading edge of the sheet impacts the front of the slot.